1. Field of the Invention
The present invention relates to a circuit arrangement for telecommunications exchange systems,particularly telephone exchange systems, comprising central and/or sub-central information processing sequential logic systems having a limited performance capability with respect to the information processing capacity, and comprising buffers preceding the sequential logic systems which equalize the information processing load of the sequential logic systems and, for this purpose, serve for a temporary acceptance of information processing requests, and comprising traffic measuring devices for recognizing information processing traffic overloads of a respective sequential logic system and for averting such overloads by way of request deviation devices influenced by the traffic measuring devices, the request deviation devices quantitatively dividing the incoming processing requests into, on the one hand, processing requests to be accepted and to be ordinarily supplied to the respective buffer and, on the other hand, processing requests not supplied to the buffer.
2. Description of the Prior Art
A circuit arrangement of the type generally set forth above is disclosed in the periodical "IEEE Transaction on Communications" September, 1973, pp. 1027 et seq. A buffer for information processing requests is generally constructed as a FIFO memory. This means that the information processing requests are sequentially output therefrom in the same sequence in which information processing requests are successively supplied thereto, in other words a first in-first out memory. In a circuit arrangement of the type set forth above, assume that the information processing requests are a matter of call-setup jobs. These arrive from subscriber stations or via trunk lines. The information processing requests on the part of subscriber stations can be a matter of a subscriber call initiating the set-up of a connection or can also be a matter of subsequently output dial identifiers which may correspond to the individual numerals of a telephone number. Information processing requests which arrive from a line terminating circuit of a trunk line occupied in a incoming manner can be a matter of a switch identifier of an incoming occupation or can be a matter of incoming selection identifiers. When a trunk line is occupied in the outgoing manner, then the end of selection identifier, the start character and the charge call counting pulses can arrive in the direction opposite that of the call set-up. These switch identifiers therefore arrive in a line terminating circuit of a trunk line occupied in an outgoing manner and likewise result in information processing requests when the respectively occupied line terminating circuit outputs toward the appertaining information processing sequential logic system.
Given central and/or sub-central information processing sequential logic systems in a circuit arrangement of the type initiall set forth, therefore, information processing requests successively arrive whose occurrence is randomly conditioned and depends on the respective subscriber behavior of each of the participating subscribers. The information processing load accordingly represents a constantly fluctuating quantity. The appertaining central and/or sub-central information processing sequential logic systems which now come of course, have a limited performance capability or call handling capacity with respect to the information processing capacity are adapted to the respectively occurring requirements in view of their performance capability. Such an adaptation of the information processing capacity to the constantly fluctuating information processing load is subject to various commands. First, an optimally high work load of a central and/or sub-central information processing sequential logic system should be achieved; this serves the purpose of an optimally high efficiency. Secondly, it must be guaranteed that the need for information processing capacity is satisfied; the proportion of connections which cannot be established due to the overload of central and/or sub-central information processing sequential logic systems should be as low as possible.
In order to meet the above requirements, the aforementioned buffers are provided in circuit arrangements of the type initially mentioned, these buffers seeing to it in a manner at the command of a person skilled in the art given fluctuating need of information processing capacity per time unit that the information processing requests are processed by the central and/or sub-central information processing sequential logic systems in succession and uniformly with respect to the information processing performance. This equalizing effect is all the more pronounced the larger such a buffer is designed and the greater the maximum waiting times between input of a respective information processing request into the buffer and fetching the same therefrom.
However, upward limits are, in turn, also placed on this waiting time. For example, a subscriber who has initiated a subscriber call by closing his subscriber line loop via his subscriber station in order to have a connection established by selecting corresponding numbers of a subscriber call number should at most have to wait only a specific time, for example one second, before he receives the dial tone after picking up the handset at his subscriber station. When he then successively outputs the various numerals of the subscriber call number he has selected, then, further, the individual numerals must be accepted at the right time by the central and/or sub-central information processing sequential logic systems. It must be guaranteed, on the one hand, that one numeral is always accepted before the next numeral arrives. In addition, it is usually even required that a numeral is accepted during the time in which it is output by the dialing subscriber, for example given audio frequency or multiple code selection methods. When it is a matter of switch identifiers which arrive in a line termination circuit of a trunk line occupied incoming, then, for example, the occupancy identifier must be processed before the first, incoming numeral of a selected subscriber call number arrives for processing.
For the reasons set forth above, therefore, the requirement also derives that the waiting time arising for individual information processing requests may not exceed a defined, upper limit. Therefore, traffic measuring devices are provided in circuit arrangements of the type set forth above, these traffic measuring devices influencing the request deviation or non-acceptance devices and effecting that the waiting information processing requests are temporarily and/or in part not accepted. Given non-acceptance of the information processing requests, it is effected in the subscriber-associated or call-associated switch device, for example in a subscriber line circuit, selection reception set, local call switching circuit or line termination circuit of a trunk line occupied incoming or outgoing, that, on the one hand, a corresponding audible signal, for example a busy signal, is transmitted to the calling subscriber and that, on the other hand, an acceptance of further switch identifiers or, respectively, their forwarding to the central and/or sub-central information processing sequential logic system is suppressed.
As already explained, the incidence of information processing requests is irregular to a certain degree, i.e. statistically distributed. This depends, on the one hand, on the individual subscriber behavior. However, an equalization in the sense of a random distribution occurs to a certain degree in a known manner due to the multitude of participating subscribers. However, random load discontinuity can thereby also occur. In addition, however, such load discontinuities can also arise due to influences shared by the group of subscribers, for example due to natural events, catastrophies, the beginning or end of a television program, times at which fee schedules change, and the like. It can also occur that the buffer is temporarily constantly full and that information processing requests are partially rejected to a corresponding degree for that time, that, i.e. call set-up of a request can partially not be fulfilled even though the connecting circuits in the switching matrix networks and the groups of trunk lines or, respectively, channels would be free. The buffer can also become full for a certain time due to internal system bottlenecks such as, for example, given temporary outage of sub-components of the same system, this likewise leading to the non-acceptance of information processing requests.